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Commit 54d5329d authored by Omar Sandoval's avatar Omar Sandoval Committed by Jens Axboe
Browse files

blk-mq-sched: fix crash in switch error path 



In elevator_switch(), if blk_mq_init_sched() fails, we attempt to fall
back to the original scheduler. However, at this point, we've already
torn down the original scheduler's tags, so this causes a crash. Doing
the fallback like the legacy elevator path is much harder for mq, so fix
it by just falling back to none, instead.

Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 93252632

block/blk-mq-sched.c

+11 −2
Original line number Diff line number Diff line
@@ -451,7 +451,7 @@ static int blk_mq_sched_alloc_tags(struct request_queue *q, 
	return ret;

}



void blk_mq_sched_teardown(struct request_queue *q)

static void blk_mq_sched_tags_teardown(struct request_queue *q)

{

	struct blk_mq_tag_set *set = q->tag_set;

	struct blk_mq_hw_ctx *hctx;
@@ -513,10 +513,19 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e) 
	return 0;



err:

	blk_mq_sched_teardown(q);

	blk_mq_sched_tags_teardown(q);

	q->elevator = NULL;

	return ret;

}



void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)

{

	if (e->type->ops.mq.exit_sched)

		e->type->ops.mq.exit_sched(e);

	blk_mq_sched_tags_teardown(q);

	q->elevator = NULL;

}



int blk_mq_sched_init(struct request_queue *q)

{

	int ret;

block/blk-mq-sched.h

+1 −1
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ void blk_mq_sched_move_to_dispatch(struct blk_mq_hw_ctx *hctx, 
			struct request *(*get_rq)(struct blk_mq_hw_ctx *));



int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e);

void blk_mq_sched_teardown(struct request_queue *q);

void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e);



int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,

			   unsigned int hctx_idx);

block/blk-mq.c

+0 −2
Original line number Diff line number Diff line
@@ -2240,8 +2240,6 @@ void blk_mq_release(struct request_queue *q) 
	struct blk_mq_hw_ctx *hctx;

	unsigned int i;



	blk_mq_sched_teardown(q);



	/* hctx kobj stays in hctx */

	queue_for_each_hw_ctx(q, hctx, i) {

		if (!hctx)

block/blk-sysfs.c

+1 −1
Original line number Diff line number Diff line
@@ -816,7 +816,7 @@ static void blk_release_queue(struct kobject *kobj) 


	if (q->elevator) {

		ioc_clear_queue(q);

		elevator_exit(q->elevator);

		elevator_exit(q, q->elevator);

	}



	blk_exit_rl(&q->root_rl);

block/elevator.c

+53 −41
Original line number Diff line number Diff line
@@ -252,11 +252,11 @@ int elevator_init(struct request_queue *q, char *name) 
}

EXPORT_SYMBOL(elevator_init);



void elevator_exit(struct elevator_queue *e)

void elevator_exit(struct request_queue *q, struct elevator_queue *e)

{

	mutex_lock(&e->sysfs_lock);

	if (e->uses_mq && e->type->ops.mq.exit_sched)

		e->type->ops.mq.exit_sched(e);

		blk_mq_exit_sched(q, e);

	else if (!e->uses_mq && e->type->ops.sq.elevator_exit_fn)

		e->type->ops.sq.elevator_exit_fn(e);

	mutex_unlock(&e->sysfs_lock);
@@ -941,6 +941,45 @@ void elv_unregister(struct elevator_type *e) 
}

EXPORT_SYMBOL_GPL(elv_unregister);



static int elevator_switch_mq(struct request_queue *q,

			      struct elevator_type *new_e)

{

	int ret;



	blk_mq_freeze_queue(q);

	blk_mq_quiesce_queue(q);



	if (q->elevator) {

		if (q->elevator->registered)

			elv_unregister_queue(q);

		ioc_clear_queue(q);

		elevator_exit(q, q->elevator);

	}



	ret = blk_mq_init_sched(q, new_e);

	if (ret)

		goto out;



	if (new_e) {

		ret = elv_register_queue(q);

		if (ret) {

			elevator_exit(q, q->elevator);

			goto out;

		}

	}



	if (new_e)

		blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);

	else

		blk_add_trace_msg(q, "elv switch: none");



out:

	blk_mq_unfreeze_queue(q);

	blk_mq_start_stopped_hw_queues(q, true);

	return ret;



}



/*

 * switch to new_e io scheduler. be careful not to introduce deadlocks -

 * we don't free the old io scheduler, before we have allocated what we
@@ -953,10 +992,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e) 
	bool old_registered = false;

	int err;



	if (q->mq_ops) {

		blk_mq_freeze_queue(q);

		blk_mq_quiesce_queue(q);

	}

	if (q->mq_ops)

		return elevator_switch_mq(q, new_e);



	/*

	 * Turn on BYPASS and drain all requests w/ elevator private data.
@@ -968,10 +1005,6 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e) 
	if (old) {

		old_registered = old->registered;



		if (old->uses_mq)

			blk_mq_sched_teardown(q);



		if (!q->mq_ops)

		blk_queue_bypass_start(q);



		/* unregister and clear all auxiliary data of the old elevator */
@@ -982,54 +1015,33 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e) 
	}



	/* allocate, init and register new elevator */

	if (q->mq_ops)

		err = blk_mq_init_sched(q, new_e);

	else

	err = new_e->ops.sq.elevator_init_fn(q, new_e);

	if (err)

		goto fail_init;



	if (new_e) {

	err = elv_register_queue(q);

	if (err)

		goto fail_register;

	}



	/* done, kill the old one and finish */

	if (old) {

		elevator_exit(old);

		if (!q->mq_ops)

		elevator_exit(q, old);

		blk_queue_bypass_end(q);

	}



	if (q->mq_ops) {

		blk_mq_unfreeze_queue(q);

		blk_mq_start_stopped_hw_queues(q, true);

	}



	if (new_e)

	blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);

	else

		blk_add_trace_msg(q, "elv switch: none");



	return 0;



fail_register:

	if (q->mq_ops)

		blk_mq_sched_teardown(q);

	elevator_exit(q->elevator);

	elevator_exit(q, q->elevator);

fail_init:

	/* switch failed, restore and re-register old elevator */

	if (old) {

		q->elevator = old;

		elv_register_queue(q);

		if (!q->mq_ops)

		blk_queue_bypass_end(q);

	}

	if (q->mq_ops) {

		blk_mq_unfreeze_queue(q);

		blk_mq_start_stopped_hw_queues(q, true);

	}



	return err;

}